Description

I thought I'd seen one somewhere in CL but I couldn't find it so here's one I made earlier ...

Ictr1 is the (LED current)*(the datasheet CTR value)/(Q1_hFE)

In this example CTR=60%

More complex models take account of the non-linearity of
the LED optical power o/p vs current characteristics and
may have detailed modelling of rise and fall times and
propagation delay.

Note that, although D1 provides a load that represents an LED,
in terms of voltage drop, resistance and junction capacitance
etc., the LED model has no optical parameters. The only
coupling to the receiver is via the behavioural current source
Ictr1 monitoring the current through D1.